"In systems where many people are free to choose between many options, a small subset of the whole will get a disproportionate amount of traffic (or attention, or income), even if no members of the system actively work towards such an outcome. This has nothing to do with moral weakness, selling out, or any other psychological explanation. The very act of choosing, spread widely enough and freely enough, creates a power law distribution."
For a much bigger look at similar effects, see Critical Mass by Philip Ball https://www.amazon.co.uk/Critical-Mass-Thing-Leads-Another/d...
I wouldn't confuse the effects of the profit motive with some nature people have for centralization.
My friends, myself and even my mother were content with the disparate isles of the net 20+ years ago.
Network effect.